The invention relates to a transportation device used primarily in a materials handling vehicle such as an industrial pallet truck.
Industrial pallet trucks typically include a drive or steer wheel located proximately under a vehicle frame of the pallet truck. The drive wheel may include a single tire or dual-tire construct. Two casters/wheels are typically employed which are located adjacent and on opposite sides of the drive wheel. The casters provide additional support of the vehicle frame weight as well as provide additional stability as the pallet truck is being turned or operated on an incline.
The pallet trucks may be powered by an electric motor or may be manually pulled or pushed by an operator. Electrically powered pallet trucks may further include a platform upon which an operator may ride during transport of a load. For an electrically powered pallet truck, the steer wheel may additionally be used as the drive wheel, such that the steer wheel also provides a traction force that drives the pallet truck.
Pallet trucks may operate in a variety of operating conditions and locations including, for example, a warehouse, truck yard, grocery store, sidewalk or even an automobile road. Operating surfaces associated with these different locations also vary significantly. For example, the pallet trucks may be required to traverse over relatively smooth paved surfaces or relatively rough unimproved and uneven surfaces such as dirt or gravel roads. Other operating surfaces may include cobbled roads or grooved or siped pavement.
As the pallet truck is moved by either an electric motor or by manual effort of an operator, the drive wheel and casters rotate in the direction of vehicle travel. As the pallet truck is operated over uneven or unimproved surfaces, the steer wheel and casters tend to move up and down in irregular patterns. As a result of the vertical movement, casters may temporarily lose contact with the ground or lose traction, making it harder to operate the vehicle. For example, if the casters lose contact with the operating surface when steering or turning around a corner, a load may move or the pallet truck may tip.
Casters that are rigidly attached to the pallet truck create an additional problem. The drive wheel may partially lose contact with the operating surface, or slip, when either of the casters travels over uneven terrain and moves vertically up and down. If the loss of pressure with the operating surface is significant enough, a loss of traction or braking ability may be experienced.
The present invention addresses these and other problems associated with the prior art.